A numerical simulation has been performed of the propagation of an action potential through a thick, cylindrical strand of cardiac tissue. The bidomain model was used to account for the effect of tissue anisotropy and the interstitial space on current flow, and the Beeler-Reuter model was used for the electrically active membrane properties. A relaxation technique was used to solve the nonlinear partial differential equations. The model has been modified to predict propagation in a 2- or 3-dimensional tissue, due to a point source of current. The influence of unequal anisotropy ratios of the intracellular and extracellular conductivities is being investigated. Pairs of stimulus pulses are applied to a 2-D sheet of tissue to create rotors and other unusual phenomena, which might be useful as models of cardiac arrhythmias and fibrillation.